The invention generally relates to robotic and other sortation systems, and relates in particular to articulated arm systems for use in sortation systems.
Systems and methods using mechanical compliance to improve robot performance during grasping and manipulation are known. Purpose-built compliant elements exist commercially that function as safety guards, such as, for example, position sensors sold by ABB Automation Technology Products AB of Sweden. These devices may include magnetic breakaway or spring elements that deflect when contact between the robot and the environment is made. Additionally, these designs can include rudimentary on/off sensing of a breakaway state, which is often used as a stop signal to the robot controller.
More modern robotic systems in industry and academia have incorporated flexible elements and deformation sensors in the joints of a robot arm (see for example, the Baxter Robot sold by Rethink Robotics, Inc. of Boston, Mass. and the DLR Lightweight Robot III developed by the Institute of Robotics and Mechanics at German Aerospace Center in Germany). Through the combined sensing of deformation at each joint, an approximation of the force at the end-effector may be deduced. Such an implementation is undesirable in certain applications however (for example, due to unnecessary added compliance that may degrade the positional accuracy of the end-effector, added mechanical complexity and cost, and decreased payload capabilities of the robotic system), with the added complication that any highly flexible end-effector on the robot arm causes the loads transmitted through to the joints to be fairly small and difficult to reliably measure.
Force sensors are also known to be used in robotic manipulation systems. A typical force sensor consists of a rigid plate instrumented with several micro-scale deformation sensors such as strain gauges. This plate is commonly placed between the robot end-effector and the robot arm, and used to sense forces and torques acting on the end-effector. These sensors tend to be expensive and difficult to calibrate accurately since they measure deflections or strain on very small scales. Furthermore, a force sensor mounted between the end-effector and robot arm suffers from the issue mentioned above for joint-sensors, namely that highly flexible elements on the end-effector will not create significant forces for detection at the force sensor.
There remains a need therefore for an improved sensing system for robotic and other sortation systems.